Known in the art is an internal combustion engine wherein an NOX storage reduction catalyst is arranged in an engine exhaust passage and a hydrocarbon feed valve is arranged upstream of the NOX storage reduction catalyst and wherein, when releasing the stored SOX from, the NOx storage reduction catalyst, the hydrocarbon feed valve supplies hydrocarbons to make the temperature of the NOx storage reduction catalyst rise, then the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is intermittently made rich to release the SOX from the NOx storage reduction catalyst (for example, see PTL 1). In this regard, if hydrocarbons are supplied upstream of the NOX storage reduction catalyst in this way, sometimes the NOx storage reduction catalyst becomes clogged. In this case, PTL 1 describes that if the NOx storage reduction catalyst becomes clogged, when hydrocarbons are supplied, compared with when not clogged, the air-fuel ratio of the exhaust gas flowing out from the NOx storage reduction catalyst becomes lean and, further, that if the NOx storage reduction catalyst becomes clogged, when hydrocarbons are supplied to make the temperature of the NOx storage reduction catalyst rise, compared with when not clogged, the speed of temperature rise of the NOx storage reduction catalyst becomes slower and therefore it can be judged from these if the NOx storage reduction catalyst has become clogged.